This invention relates generally to the field of telecommunications and, more particularly, to a system and method for processing an input signal communicated on a telephone line.
Digital subscriber line (DSL) technologies allow existing twisted-pair telephone lines to communicate both analog telephone signals and digital data signals between, for example, network equipment at a central office and subscribers at remote locations. Typically, the telephone signal is communicated using a frequency band between approximately 300 Hz and approximately 3.5 kHz, and the data signal is communicated using a frequency band above approximately 25 kHz. At both the central office and a subscriber""s remote location, a plain old telephone service (POTS) splitter may receive an input signal from a telephone line and separate telephone and data signals from the input signal using low-pass and high-pass filters, respectively. In addition, the POTS splitter may attenuates the spectral power from a DSL modem output to a telephone device input.
In general, a POTS splitter should satisfy two fundamental requirements to operate optimally in conjunction with a typical telephone device and a typical DSL modem. First, to avoid interfering with or degrading the quality of basic telephone services, the POTS splitter should have a characteristic impedance that suitably matches or approximates the impedance of the telephone line and the telephone device, which is typically approximately 900xcexa9. Second, because the high-pass filter used to separate the data signals from the input signal typically has an approximately 50-60 nF capacitance to accommodate the relatively low input impedance of the DSL modem, the POTS splitter should suitably absorb this 50-60 nF capacitance.
As individuals, organizations, businesses, and governments continue to transition from a post-industrial economy to an information-based economy, their communication needs continue to grow. Consequently, telecommunications service providers must strive to communicate an increasing amount of information over existing twisted-pair telephone lines. For example, in many European markets, service providers use additional tones or other suitable signals, usually at an intermediate frequency of either approximately 12 kHz or approximately 16 kHz, to communicate tax, billing, or other information associated with telephone calls. Service providers in other markets may have similar needs. Unfortunately, telecommunications equipment manufacturers have been unable to provide a cost-effective POTS splitter to efficiently separate these additional signals of intermediate frequencies from input signals that are transmitted over telephone lines and contains low and high frequency components associated with telephone and data signals, respectively. More particularly, previous POTS splitters cannot adequately satisfy the two fundamental requirements described above while passing intermediate frequencies above approximately 6-8 kHz, such as those typically associated with tax, billing, or other information related to calls. As a result, previous POTS splitters are increasingly inadequate for many applications.
According to the present invention, the disadvantages and problems associated with the processing of an input signal communicated on a telephone line have been substantially reduced or eliminated.
According to one embodiment of the present invention, a system for processing an input signal communicated on a telephone line includes an input node to receive the input signal. The input signal comprises a first component associated with a first frequency band, a second component associated with a second frequency band higher than the first frequency band, and a third component associated with a third frequency band higher than the second frequency band. A first filter coupled to the input node receives the input signal, attenuates the first and third components, and communicates a first signal substantially comprising the second component. A second filter coupled to the input node receives the input signal, attenuates the second component, and communicates a second signal substantially comprising the first and third components. A third filter coupled to the second filter receives the second signal, attenuates the third component, and communicates a third signal substantially comprising the first component. An intermediate node coupled between the second and the third filter may also couple to a fourth filter having an input capacitance that limits the ability of the third filter to pass the second component. In a more particular embodiment, the system is a POTS splitter, the first component is an analog telephone signal, the second component is tax/billing tones, and the third component is a digital data signal.
The system and method of the present invention provide a number of important technical advantages. In one embodiment, the present invention may provide a POTS splitter with a characteristic impedance up to approximately 900xcexa9 that can suitably absorb a capacitance of approximately 50-60 nF while passing intermediate frequencies above approximately 6-8 kHz. As a result, the POTS splitter of the present invention is able to receive from a telephone line an input signal that contains an analog telephone signal in a first frequency band, tax/billing tone is a second frequency band higher than the first frequency band, and a digital data signal in a third frequency band higher than the second frequency band; process the input signal; communicate an output signal including the telephone signal and the tax/billing tones; and communicate another output signal including the data signal. Other technical advantages are readily apparent to those skilled in the art.